The present invention relates to a new and improved method of making a mold for forming a cast product having a plurality of spaced apart surface areas. The method is advantageously used to form a mold for a plurality of airfoils which are disposed in a circular array.
Turbojet engines commonly include cast components having a plurality of airfoils disposed in a circular array about either a hub which may be rotatable or an outer ring which may be fixed to the casing of the jet engine. Known methods of forming molds for a jet engine component are disclosed in U.S. Pat. Nos. 3,669,177 and 3,848,654. The mold making methods disclosed in these patents contemplate that a plurality of wax airfoil pattern segments will be disposed in a circular array. The pattern segments are then connected together to form a unitary ring by the application of adhesive or hot wax to surfaces of the airfoil pattern segments at joints between the segments.
The application of hot wax or adhesive to the joints between the various airfoil pattern segments is a time consuming process which requires a high degree of manual dexterity. If the hot wax or adhesive is not properly applied at the joints between the pattern segments, imperfections are formed in the cast part. Even if the imperfections are not of such a degree as to require scrapping of the cast part, the correcting of the imperfection further contributes to the cost of forming the part.
Once the airfoil pattern segments have been interconnected in a circular array as disclosed in the aforementioned patents, the circular array of airfoil pattern segments is repetitively dipped in a liquid ceramic mold material. Due to the fact that the airfoil pattern segments are formed of wax and are interconnected by wax at joints between the segments, the circular array of airfoil pattern segments tends to deflect under the influence of forces applied to it as it is repetitively dipped in the liquid ceramic mold material. Of course, any deflection of the airfoil pattern segments impairs the accuracy with which the resulting mold and casting are formed. Pattern materials have been reinforced by the use of a rigid reinforcing member in the pattern material in the manner disclosed in U.S. patent application Ser. No. 676,227 filed Apr. 12, 1976 by William S. Blazek and entitled "Method of Making A Mold".
Another known method of making a mold for casting a component of a jet engine is disclosed in U.S. Pat. No. 4,066,116, issued Jan. 29, 1976, by William S. Blazek et al and entitled "Mold Assembly and Method of Making the Same". This patent discloses a mold having a plurality of separate sections for forming airfoils. Sections of the mold in which an airfoil is formed are made by coating a wax airfoil pattern with a ceramic mold material. The wet coating of ceramic mold material is dried and the pattern destroyed to form a pair of airfoil mold sections which are interconnected to form an airfoil mold cavity. The airfoil mold sections are then connected to hub and ring mold sections to form a mold assembly.